The field of the disclosure relates generally to operation of gates at grade crossings, and more specifically, to systems and methods for vehicle detection at island crossings.
Train traffic in North America typically intersects with public streets and highways at rail grade crossings. At such crossings, active and/or passive warning systems provide a notification to automotive traffic regarding the impending arrival of a train. The particular notifications provided are somewhat dependent on the street or highway intersecting the rail line. For example, where average train speeds or automotive traffic volume warrants, active warning systems are deployed which may include one or more of flashing lights, bells, and barrier gates. As high speed rail infrastructure is expanded to promote high-speed intercity passenger service, more attention is being paid to the performance of these warning systems.
While the active warning systems are effective, risks persist. One such risk is that associated with the instance of vehicles that are found within the crossing island, which is the area between barrier gates where the rails are located. Such vehicles may be accidently or deliberately placed in such crossing islands. For example, a vehicle may become disabled while within the crossing island. Instances have occurred where automobile drivers have driven around the barrier gates only to find themselves trapped within the crossing island.
High mass freight trains, at speeds of 55 miles per hour and greater take thousands of meters to halt, a situation that becomes more perilous with a current emphasis on development of high-speed rail traffic (80-110 MPH (grade separation is required above 110 MPH)). At such speeds, locomotive operators and engineers have insufficient time to halt the train if such an obstruction such as a disabled vehicle is visually identified at an upcoming crossing.
As mentioned above, active railroad crossing warning systems typically utilize barrier gates and flashing warning lights. A key objective of the North American high speed rail initiative is increasingly higher speed rail traffic in a mixed operating environment with conventional freight equipment and service, in many cases in double and triple track corridors. At the majority of the 60,000+ active railroad crossings within the U.S., railroads have typically utilized two quadrant gate warning systems—comprised of entrance gates in front of traffic entering the crossing ‘island’ but with no exit gate so that any vehicles entering or within the crossing island when the gates start to descend have a clear and unobstructed exit path.
With the advent of higher speed locomotives, especially those traveling at 80-110 MPH, it is necessary to utilize four gates—two entrance gates augmented by two exit gates—to completely seal the corridor during train movement across the crossing. While the ‘fail-safe’ position of entrance gates is in the lowered position, the fail-safe position of the exit gates is typically in the raised position to prevent any vehicles from being trapped in the crossing island when the crossing is activated and the roadways are closed off.
Initially, exit gates were programmed to delay several seconds before descending, allowing an arbitrary time period for any vehicles on the island to exit the crossing. Such a system is sometimes referred to as Timed Exit Gate Operating Mode or Timed EGOM. However, studies have since shown that it is necessary to detect vehicles in the crossing to maximize safety. With vehicle presence detection, exit gate descent is delayed until it can be verified that all vehicles have cleared the crossing, and a particular exit gate may be raised (or stay raised) if it can be determined that a vehicle is in the island in a corresponding lane of traffic. This type of system is sometimes referred to as a Dynamic Exit Gate Operating Mode or Dynamic EGOM).
The primary vehicle detection technology accepted for use today is a sub-surface inductive loop array, with a proven reliability as illustrated by its popularity in traffic intersection controls. Continuity verification and periodic check loop tests are utilized to provide an indication, although not comprehensive verification of loop array operation and performance. A failure of one or more loops in a crossing island implementation typically informs an exit gate controller system, causing it to revert to a simplistic time delay mode of operation that incurs a safety risk for high-speed rail environments. While buried inductive loops are effective at detecting the metallic content of vehicles entering an intersection or railroad-crossing island, certain drawbacks have compelled railroad organizations to seek alternative solutions, including the following:
For example, repair of sub-surface inductive loop systems is problematic and time consuming, requiring coordination by both the railroad and local highway maintenance organizations. Installation or repair of loops in a highway-rail grade crossing island is disruptive to both vehicular and railroad traffic requiring that trains slow to a safe speed or in some cases stop and post a flagman prior to passing through the crossing. In high-density urban freight corridors where there may be in excess of 100 trains per day, the financial and congestion consequences (for both vehicular and railroad traffic) are intolerable.
Inductive loop arrays are not fully adequate for triple track sites where internal track spacing complicates installation and reduces the size of detection zones within the crossing island. The restricted space allowable for inductive loops, especially between adjacent tracks, has the consequence of lessening the sensitivity of the loop. A function of the physics associated with inductive loop detection, the detection height of a loop is ⅔ of the length of the shortest side of the rectangular loop. Therefore, since space between tracks restricts the loops' short side dimension, there is a corresponding decrease in detection height and sensitivity. This drawback is exacerbated when pre-formed concrete or composite panels are used as a crossing roadbed, because of the limited rectangular area available for inductive loop installation.
Further inductive loops lack an inherent capability for in-service functional checks or any means of active redundancy. Because of the magnetic principals involved, loop systems cannot include redundant, concentrically arranged loops. Therefore, two redundant systems cannot be constantly compared for identical response, which would provide constant, in service performance verification. Instead, loop systems typically employ ‘check loops’ which are buried alongside the primary detection loops and which are briefly excited at programmable intervals (from one to 200 or more minutes) with a frequency that can be picked up by the detection loop. In actuality, check loops only verify detector loop continuity and only imply an ability to detect a vehicle passing overhead, and lack any means of quantitatively evaluating detection loop sensitivity or signal to noise immunity. A failed check loop sequence can be the result of a failed detector loop or a failed check clip and therefore is somewhat ambiguous.
A number of different technologies and methods have been used for vehicle detection, with varying degrees of success. While some applications can justify the relative lack of reliability these detection methods achieve (for instance, parking lot gates and traffic light violation detection), they do not qualify for the safety critical requirements of railroad crossing.
Video image processing is one such technology. For example, a video camera and sophisticated image processing can locate vehicles in a real time image using video processing, or analytics. Video systems are costly relative to loop and the radar technologies, but their greatest drawback is poor performance in low light, very bright light, and during inclement weather where rain, snow, and fog can limit visibility. Video processors are not regarded as a sufficiently reliable or cost-effective detection technology to influence the behavior of railroad crossing warning systems.
Doppler microwave detectors are continuous wave (CW) Doppler devices that transmit bursts of energy at a fixed frequency between 1 and 40 GHz. When a vehicle passes through this signal a portion is reflected back to the emitter, slightly shifting the frequency based on the vehicle's speed (Doppler shift). CW microwave radars are therefore only able to detect vehicles that are moving. In addition, the majority of microwave radars utilize a single beam, which is aimed and directed by way of a physical antenna “horn” that focuses the detection beam on the area of interest. To cover the large rectangular detection area presented by a typical railroad crossing would require electronic or mechanical steering of the beam or the use of multiple single beam radars operating in concert and configured to prevent cross-radar interference. While technically feasible the life-cycle cost and maintenance of electronic or mechanically steered radars is not practical for railroad crossing applications. This is also the case with Ultra Wide Band, Micropower Impulse Radar approaches.
Infrared detectors are most commonly used in commercial and residential security systems. Active IR illuminates a detection zone with low power infrared energy (just above visible light spectrum). Objects in the detection zone reflect the signal back where subsequent processing determines presence. Passive IR relies on changes in the thermal content of the detection zone, caused by objects that are warmer or cooler, from an infrared wavelength perspective, than the surrounding area. Several disadvantages of infrared detectors are often cited. With active devices, atmospheric effects may cause scatter of the transmitted beam and received energy. Glint from sunlight may cause unwanted and confusing signals. With respect to weather, the amount of energy reaching the focal plane is sensitive to water from fog, haze, and rain, as well as to other obscurants such as smoke and dust. In addition to scattering, these environmental effects can absorb energy that would otherwise be detected by both active and passive infrared devices. As such, infrared technologies are not considered a sufficiently viable detection technology to influence the behavior of railroad crossing warning systems.
Ultrasonic vehicle detectors can be configured to receive range and Doppler speed data, the same concept used by the radar detectors, but at a much lower frequency and issued as sound waves rather than radio waves. Ultrasonic detectors transmit sound waves, at a selected frequency between 20 and 65 kHz, from overhead transducers into an area defined by the transmitter's beam width pattern. A portion of the energy is backscattered or reflected from the road surface or a vehicle in the field of view. While useful for measuring tank levels and other closed environment sensing, ultrasonic sensors have not delivered sufficiently reliability to qualify for railroad crossing use due to limited range and interference from ambient noise sources.
With regard to passive acoustical detector arrays, vehicles produce acoustic energy or audible sounds from a variety of sources within each vehicle and from the interaction of the vehicle's tires with the road. Although unintentional, the radiated sound acts as a beacon signal containing information that can be extracted by roadside acoustic energy detectors. Arrays of passive acoustic microphones can isolate and provide spatial directivity from which sounds are continuously detected and processed from a specific location along the roadway. However, the chaotic acoustical environment at a crossing and the wide array of vehicle signatures that must be adaptively classified and processed render this technology inadequate for a railroad crossing application.
Magnetic detectors indicate the presence of a metallic object by the disruption it causes in an induced or natural magnetic field. These detectors may be active devices (magnetometers), or passive devices (magnetic detectors). Individual magnetometer cylinders must be buried a numerous locations in the detection area. They are powered by batteries and signal presence detection to a nearby collector receiving signals from the entire sensor array. The complexity of the local area wireless network, intrusive installation labor, and the need to periodically replace batteries makes this technology unsuitable. In addition it has been found that the considerable magnetic mass of a locomotive creates a magnetic ‘memory’, degrading the sensors' sensitivity for periods of time after a train has passed the detection zone.